Coaxial line stub support



Sept. 18, 1951 .1. GOLDSMITH COAXIAL LINE STUB SUPPORT Filed Feb. 15,1944 V 7 3% ..0 Mm h P u Patented Sept. 18, 1951 COAXIAL LINE STUBSUPPORT Joseph Goldsmith, Newton, Mass., assignor to RaytheonManufacturing Company, Newton, Mass., a corporation of DelawareApplication February 15, 1944, Serial No. 522,489

5 Claims.

This invention relates to coaxial transmission lines, and moreparticularly to a novel means for supporting the central conductor ofsuch lines in proper alignment with the surrounding outer conductor.

Heretofore various means have been proposed for supporting the centralconductor of a coaxial line relative to the outer conductor. One of themost common means involves the use of insulating disks or beads throughwhich the central conductor extends, and which have a tight fit withinthe outer conductor. Such constructions introduce dielectric losses andelectrical discontinuities in the line due to the difference in thedielectric constant of the insulating disks and the air between thedisks. lines are not simple in construction since the disks must bespaced at predetermined distances apart and it is difficult to preventdisplacement of the disks along the line. In cases where the line mustextend vertically, as for example to an elevated antenna structure, thedisks must be rigidly fixed with respect to the transmission line.

To avoid such difficulties, it has been proposed to support the centralconductor by means of stub supports, each stub constituting a branchline having a length approximately equal to onequarter of the length ofthe waves on the transmission line. Such stub supports, while affordingsatisfactory alignment of the central conductor, possess manydisadvantages. Inasmuch as the stub lines project beyond thecircumference of the outer conductor for a substantial distance, theoverall dimensions of the transmission lines are greatly increased andits bulk and weight become excessive. Due to the many stub linesprojecting radially in all directions from the transmission line, theline becomes difficult to install in any place where space is a materialconsideration.

It is among the objects of the invention to avoid the difficultiesinherent in conventional structures ofthe type described and to providea struc-. ture which obviates the necessity for introducingsupportingdisks of dielectric material into the transmission line or for providingnumerous stub lines projecting therefrom.

, It is also among the objects of the present invention to provide ahigh frequency transmission line capable of transmitting waves of highfrequency over a relatively wide frequency range without substantialdifferences in the attenuation of the waves.

It is a further object of the invention to provide a high frequencytransmission line which 'is Furthermore, such I simple in constructionand manufacture, and in structed in. accordance with the present inven-'tion; and I Fig. 2 represents a transverse section taken on the line 2-2of Fig. 1.

In the drawing reference numeral I indicates a section of the outertubular conductor of a coaxial transmission line having a centralconductor 2. At points where the central conductor is to be supported bythe outer conductor, a portion of the outerconductor I is'cut away and ablock 3 is inserted in the opening so formed, which block partiallyobstructs the free space between the outer conductor I and the innerconductor 2. The block 3 is of conductive material and is rigidlyconnected to the outer conductor I, as, for example, by soldering, andcompletely closes the opening in the outer conductor I. A screw bolt 4extends through the block 3 and is threaded into an insert 5 secured inthe central conductor 2 at an enlarged portion 6 thereof. The enlargedportion 6 extends for a distance approximately equal to one-half of thelength of the waves on the transmission line. The insert 5 is ofconductive material and is secured to the conductor 2 at the enlargedportion 6 in a manner to provide both a good electrical and rigidmechanical connection therewith, The insert ,5 is of substantially thesame diameter asthe unenlarged portion of the conductor 2 andconstitutes a rigid metallic connector functioning as a branch fromconductor 2 electrically connected to the conductor I at the block 3. Agood electrical connection may be secured between the insert 5 and block3 by soldering the joint therebetween after the parts have been securedin position by the bolt 4.

It has been found that the construction de-. scribed providessubstantially reflectionless trans.- mission of high frequency wavescovering a -rela-.

V tively wide-range of frequencies and will transmit power of the ,orderof one megawatt without break-down. For example, in a fifty ohm linemensioned to suit the particular portion of the-- high frequencyspectrum employed Inany par,- ticular case the impedance provided by theenlargement 6 or equivalent element; on theconductor 2 and by the block3 or equivalent. elementon the conductor I will be proportioned tomatch:

under the particular operation conditions and,

cancel out reflections resulting from the support to securesubstantially refiectionless transmission within the frequency rangewhich the line is adapted .to; transmit;

r In the determination ofthe.dimensions of the parts-for any: particularf -requencyran e; itv will besimpler in, most; instances; for-thoseskilled in the; art: to determine; these byrdirect. electricalmeasurement of; reflection; than to predeterminethem; by. analysis. Inmaking such; determinations; it Willi-be helpful; o consider thefunctions ofiathe enlargement Ii separatelyfrom its functions; incombinationwith the block; 3. Ifga d-i-. rect connection ismade'between;theconductor 2 and: the; conductor 1' by; a branchconnectorsuch its-: without: theenlar ment i andiw cutr block: 3, for?substantially all; frequencies the. impedance along the connector is notinfinite and: will; beg ieilections from the connector. When anenlargement 6 is; provided. extendingfprapnrcxircatetv neua ter;avelength: on

e chde .Q he nt nrcf: the conn ct r then,

scmec r the-- r flectio s are cance evcrr out thetimpedanceyprpvidedby-the;b1ock 3;; Un-.

dentihese nditi n tha ni re mc t- 6 unct s asa. trans r r; to greatly:incre sehe mp dr agree, and; substantially decrease: the; reflections;0min. other: words-L to introduce a compensating impedance tending to;match, the impedance in-.

troduced'. by the connector- 5;.-and thus tending to make-the. lumped:impedance of the connecting structure infinite. Where the transformer(idoes,

not produce an infinite lumped impedance, the block=-3; orsomeequivalent impedance, is pro! vided in addition to the enlargement 6.Underthese conditions the. impedance becomes infinite and there will beno reflections. Thus, the enlargement-wand the block 3 function asmatching impedances, and when matched to the. im-. pedanceintroducedbytheconnector 5: the. im-. ped'ance across the-line becomes infinitewhile substantially no impedance is offered. bythe-supportinthedirection of 'the line.

Thus,- while the enlargement- 6 may of itself reduce the electricaldiscontinuities introduced in the line by the branch connector 5-,I'prefertosupply;- a; coasting impedance, such as block 3', in thepreferredarrangement shown.

an exampleof the preferred; arrangement, incne commercially successfulembodiment of the invention, in a line operating upon a wave length of9.8 centimeters, the following dimensions were used, The internaldiameter ofthe conductor I was 1.527"; the diameter of the centralconductor was %",,the diameter of the enlargement 6- was qt'z'zaf', andits length was 1.950. The length QL-t ebl ck, in th irecti n. ofthenline, w s

4 1.250". This projected into the line for a maximum distance of 0.287".

It will be observed that because of the great mechanical strength andrigidity of the support, only a few such supports need be provided alonga substantial length of the transmission line in order to secure andmaintain the desired alignment of the conductors. Thus, unlike priorconstructions, but a small number of supports are essential. However,where desired, the supports may be spaced one-half wave length apart orat any distance greater than one-half wave length.

It will be obvious that many departures may be made from the specificdetails shown. For example, the enlargement 6 need not be formedintegral with the. line 2 but may be formed as a separate sleeve andshrunk on or otherwise secured in intimate contact with the conductor 2.Similarly parts such as the insert 5 may, where convenient, be formedintegrally with the cond-uctor-Zorrtheenlargement 6.

While I have shown aparticular embodiment; of :-the invention, otherembodiments andmodi ficationswithin thescope of the appended claims willbe apparent to those skilled in the art from, a consideration of thestructure shown andteachnssh rei What, isv claimed is:

1 An electric-transmission line for transmit ting; high frequencyelectricwaves including a,tu bular, conductor, a central conductorcoaxial with said tubular conductor, means for maintaining saidconductors in fixed. spaced relation compr se, ing a metallicconnectorbetweensaid conductors; said, central. conductor having an.enlargement, thereon, andmeans projecting inwardly from said,tubularconductor partially obstructing the space between said conductorsfor cancelling, reflec,-. t cns, r su tin m sa d c nn or.

2-. Anelectric transmission line for transmit; ting, high, frequencyelectric waves, including, a, tubulanconductor, a central conductorcoaxial, with, said, tubular conductor, meansfor maintain; ing said,conductors in fixed spacedrelationcom- 1 p i n a metal c connectorbetween said, c9

ductors, said central conductor having an en,- largement. thereonextending for a distancev ap proximately equal to one-half of, thelengthof the, waves. on saidtransmission line, said con nector beingconnected to said, central conductor; a said lar em nt, an means pr j ctng n; war ll frcmsaid. tubular ondu tor. or. pa l c lrv bst uct ev pabetwe n. s id cn uc cn saidv proj ction and said enlargement being pro;pcrticned to sub ta al y canc th reflection resulting fromsaidconnector.

3. An electric transmission line for transmitting high frequencyelectric waves including a; tubular conductor, a central conductorcoaxial; with said tubular conductor, said tubular conductor having anopening therein, a block rigidly connected to said tubular conductorclosing said opening and partially obstructing the space be tween saidconductors, said central conductor; having an enlargement thereon, andmeans providing a supporting connection between said bloc and" theenlarged portion of said central con,- ductor.

4. An electric transmission line for transmit-1 ting high frequencyelectric waves including a tubular conductor, a central, conductorcoaxial; with said tubular conductor, said tubular conductor having anopening therein, a metallic block rigidly connected to said tubularconductor' closing said opening and partially obstructing. the spacepetween said conductors, said central conductorhailing an emargementthereon and extending for a'g distance approximately equal to one-half}ofthe rlength of the waves on said transmission line, and a metalconnector of substantially the same diameter as said central con-'ductor providingha supporting connectionbetween said block andtneenlarged portion of said central conductor.

5. An electric transmission line for transmitting high :E'req iencyelectric waves including a tubular condiieton-ja central conductorcoaxial with said tubiilaf conductor and braving an enlargement thereon;{a metallic connectofi between said tubularcqndiictor and saidenlargement for maintaining; said conductors in fixed spacedrelationship jsaid connector including portions extending inwardly fromsaid tubular conductor toward but terminating in spaced relation to saidinner conductor for preventing reflections resulting from 'saidconnector.

JOSEPH GOLDSMITH.

z REFERENCES CITED The-following references are of record in the fileofi this "patent:

UNITED STATES PATENTS Number Name Date 2,284,529 1 Mason May 1,26, 19422,408,745 Espley Oct. 8, 1946 2,446,982 Pound Aug. 10, 1948

